The present invention relates to the field of powder materials, and more specifically to the making of fine powders. For the purpose of this description some non-limiting examples of fine powders may include those classified as fine, ultrafine, nanofine; etc.
Powders are being used increasingly in a variety of applications. Some non limiting examples of those applications include molded parts, coatings, printing inks, pigments, and electrical media. Generally speaking, the finer the size of the powder the better the resulting properties and/or manufacturing results. Fine powders or particles perform better than coarse powders or particles because:    a. Fine powders have more surface area and, thus, more energy per unit of weight.    b. Fine powders absorb electrical and magnetic energy better than coarse powders.    c Molded parts made from fine powders reach higher densities during compaction and/or heating, and require much less time and, therefore, energy to do so. Higher density results in better mechanical properties;    d. Molded parts made from fine powders have smaller grain size after compaction and/or heating, which also results in better mechanical properties; and molded parts made from fine powders have smoother surfaces and better surface detail.
It has been found that, fine powders are not always easily or commercially available. It has also been found that fine powders are expensive due to the complexity or labor intensive manufacturing methods. And, in many cases, the available fine powders are impure because of contamination that occurs during processing, for example grinding.
Spherical, fine powders are even more desirable than other shapes for many applications noted above. In addition to the advantages listed above for fine powders, fine spherical powders flow and pack better than non-spherical powders, and in the case of injection molding processes, fine spherical powder is optimal for achieving the paste properties needed for properly molding parts. However, sphericity typically occurs only when coarse feed powders or particles are heated above their melting points and then are allowed to solidify without contacting other matter with which the particles will react or interact. These conditions are difficult to meet, particularly for materials with high melting points, or which are extremely reactive in their molten states. As a result, fine spherical powders generally are not available on a commercial basis for many materials.
While conventions for describing powders by size have not been rigorously defined, powders typically are considered “coarse” if they are greater than 45 micrometers in diameter, “fine” if they are greater than 20 and less than 45 micrometers in diameter, “ultra fine” if they are less than 20 and greater than 1 micrometers in diameter, and “nanofine” if they are less than 1 micrometer in diameter. For the purposes of this application, the word “fine” is used to mean fine, ultra fine, and nano powders as described except when context requires, and use of quotations around a description of powder by size indicates, otherwise.